1. Field of the Invention
The present invention is related to a two-cycle engine.
2. Description of Related Art
Conventionally, a two-cycle engine including an engine body, a carburetor, and an inlet pipe that connects the engine body and the carburetor is known. Being simple in mechanism and light in weight, such a two-cycle engine is often installed in a portable work machine such as a chain saw.
In the engine, a fuel ingredient in a mixture gas adheres on an inner wall of an inlet pipe. When negative pressure in the inlet pipe is elevated, this fuel (fuel ingredient) is suctioned into the engine body. Such a suction causes an excessive fuel delivery to flow into the engine body until fuel is delivered again in a standard amount, lowering the number of revolutions and thus making the engine unstable. Such an excessive suction of fuel by the engine may occur periodically, Besides, when a posture of a portable work machine in which the engine is installed changes, fuel (mixture gas) staying in the inlet pipe flows into the engine body, which is another cause of the fluctuation of the number of revolutions.
In view of the above, fluctuation of the revolutions have conventionally been restrained by increasing the revolving inertia of the engine with a flywheel or the like. However, in recent years, an engine without a flywheel or the like is occasionally employed for weight reduction. Because the revolving inertia of such an engine is small, the fluctuation of the revolutions cannot be restrained by the revolving inertia.
To solve the problem, an engine in which a large number of projections shaped in tetrangular pyramids are provided on the inner wall of the inlet pipe is known (e.g., Document 1: JP-A-62-206263). In the engine of Document 1, the projections can restrain the fuel adhering on the inner wall of the inlet pipe from flowing toward the engine body, so that the fluctuation of the number of revolutions can be restrained.
However, with the engine of Document 1, flow of the fuel (mixture gas) staying in the inlet pipe into the engine body due to change in posture of the portable work machine in which the engine is installed cannot be sufficiently prevented In addition, when the negative pressure in the inlet pipe is elevated, the fuel adhering on the inner wall of the inlet pipe inevitably flows into the engine though the flow amount may be small. Therefore, improvement can be made to the engine of Document 1 with in terms of restraining fluctuation of the number of revolutions.